CREATE SEQUENCE emp_s
          INCREMENT BY 1 -- 每次加几个
          START WITH 10 -- 从1开始计数
          NOMAXVALUE -- 不设置最大值
          NOCYCLE -- 一直累加，不循环
          NOCACHE -- 不建缓冲区
          
CREATE SEQUENCE s_time
          INCREMENT BY 1 -- 每次加几个
          START WITH 10 -- 从1开始计数
          NOMAXVALUE -- 不设置最大值
          NOCYCLE -- 一直累加，不循环
          NOCACHE -- 不建缓冲区
          
trigger emp1  
   before insert on "HR"."HR_EMPLOYEE" 
   for each row 
begin  
   if inserting then 
      if :NEW."EMP_ID" is null then 
         select EMP_S.nextval into :NEW."EMP_ID" from dual; 
      end if; 
   end if; 
end;

trigger time1  
   before insert on "HR"."HR_TIME" 
   for each row 
begin  
   if inserting then 
      if :NEW."ID" is null then 
         select S_TIME.nextval into :NEW."ID" from dual; 
      end if; 
   end if; 
end;
